1. Field of the Invention
This application concerns an electromagnetically actuated type of fuel injector and its method of assembly and calibration. The subject injector design includes a generally tubular housing with open ends permitting end insertion of an actuator subassembly into one end and a valving subassembly into the opposite end. The valving subassembly is axially positioned relative to the housing to define a predetermined maximum opening followed by attachment of the subassembly to the housing. This calibration method accurately establishes the flow rate for the fuel injector.
2. Description of Related Art
It is important in the design of fuel injectors to provide a device which is both easy to assemble and then calibrate resulting in consistent operational characteristics, such as flow rates.
By necessity, a modern electromagnetically actuated fuel injector has a many parts. Assembling each part one after another is very undesirable. The resultant complex structure leads to inaccuracies caused by stacking of normal tolerances. As a result, the fuel injector is difficult to accurately calibrate.
An example of a fuel injector design that is thought to be relatively difficult to assemble and to calibrate includes the devices disclosed in U.S. Pat. Nos. 4,245,789; 4,247,052; 4,231,525; and 4,342,427. One end of the fuel injector housing receives: a bobbin assembly; a pole piece assembly; and a spring calibration and armature guide assembly. A second end of the injector housing receives: an armature; a valve seat assembly; and a threaded calibration member. To calibrate the injector, the armature position is established by one adjustment while the location of the valve seat relative to the valve is established by another adjustment.
The fuel injector disclosed in U.S. Pat. No. 4,331,317 utilizes a housing's interior spacer to establish a desired axial positioning of both an armature to core and a valve to valve seat calibration. In addition, a pressed-in member establishes the position of a spring support. The fuel injectors disclosed in U.S. Pat. Nos. 4,331,317 and in 4,520,962 use a spacer-stopper for calibration. Also, a spring position is established by a separate adjustment.